1. Field of the Invention
The present invention relates to a method for neutralizing mercury derived from dental amalgams. More particularly, the invention pertains to the use of sulfur for inhibiting the harmful effects of mercury caused by the leaching of mercury from amalgam fillings.
2. Description of the Prior Art
Amalgams or alloys of metal powders composed mainly of silver and mercury have long been used as dental filling materials. Dental amalgams as hardenable mixtures are prepared by triturating or mixing silver based alloys with liquid mercury. These initially pliable mixtures are filled into teeth cavities where they set to a hard mass after a time at mouth temperatures by an amalgamation reaction between the mercury and silver or other metal components. Due to the fact that such amalgams yield strengths durable to occlusal pressures, have good workability in preparation, and have an external configuration consistent with the remainder of the tooth, they have been commercialized for dental restorations up to the present.
However, recent studies show that dental amalgams do not have the characteristic durability and permanence that earlier distinguished these filling materials. It has now been found that conventional dental amalgams have a thermal expansion significantly different than that of the tooth. Consequently, when hot and cold foods or liquids come in contact with the restored tooth, the differences in expansion and contraction between the tooth structure and the amalgam cause mercury leakage around the margin of the fillings examined.
It was also found that mercury is released from silver-tin amalgam restorations by such factors as differential aeration. Differential aeration is a common oxidative phenomenon that causes corrosion or tin dissolution to occur in areas at the restoration-tooth interface. Over a period of time, the tin dissolves or corrodes because tin is less noble and therefore more easily oxidized than either Ag or Hg. The net effect is that the oxidation of tin atoms results in tin ions within the interface. This reduces the strength of the amalgam restoration and contributes to partial extrusion of the restoration from the cavity. In addition, the presence of tin ions in the area adjacent to the cavity surfaces promotes ionization of mercury which substantially increases the tendency for the mercury to vaporize subsequent to leaching from the amalgam restorations.
It is well known that mercury is essentially a harmful substance to which severe environmental standards are applied. The maximum permitted mercury content of air is 0.05 mg/m.sup.3. Mercury vapor is colorless and odorless and therefore difficult to detect. The toxic effect of its inhaled vapors has been formerly known to be injurious to health. More recently, the dissolution of mercury from amalgam fillings has been causally linked to mercury poisoning according to several researchers. Also, it has been confirmed that dental amalgams come in contact with oral fluids during setting, such that the harmful mercury leaches and accumulate in various organs of the body. Mercury from the oval cavity passes through the cells and into the blood. Because of its high solubility in the lipoids, mercury will dispense readily to the brain, liver and kidneys with a half-life of more than 40 days.
Tests conducted on individuals with amalgam fillings revealed that the level of mercury present in the gases of expiration exceeded the permitted level in many of the cases investigated. It has been reported that the level of mercury concentration in the oral cavity increases with brushing of the teeth. Also, chewing chewing-gum reportedly gave rise to a substantial increase in the mercury content. The physiological symptoms associated with low-level exposure to toxic mercury include headaches, tiredness, loss of memory and other mental disturbances. Higher exposures result in more serious injury, such as cardiac problems and neurological ailments.